Smooth slow moving image interpolation playing is a playing method of receiving a moving image having a certain frame rate and smoothly performing playing at a speed slower than a certain speed. In this playing method, a motion search is performed on an input original image, an interpolated image is generated using the motion vector, and display is performed inserting the interpolated image between the frames of the original image. Thus, it is possible to prevent the same frame of the original image from being displayed multiple times and implement smooth slow playing.
As a process similar to the smooth slow moving image interpolation playing, there is frame rate conversion (FRC) based on motion compensation. This is a process of converting a moving image having a first frame rate into a moving image having a second frame rate. For example, it corresponds to a process of converting a frame rate of 60 fps into 120 fps that is twice the frame rate when a moving image of a frame rate of 60 fps is displayed on a liquid crystal panel having a display capability of 120 fps. At this time, the image having the second frame rate is obtained by generating an interpolated frame based on motion compensation and inserting the interpolated image between the frames of the original image. Through this operation, the converted moving image is more smoothly displayed.
Meanwhile, there are cases in which a scene change is contained in a moving image. When an interpolated image is generated using the frames before and after the scene change, motion compensation is performed using images having no correlation, and so a distorted image is generated.
In this regard, in the FRC process, when a scene change is detected, a process different from normal interpolation is performed. For example, when a scene change is detected, a frame preceding or following the scene change in time is inserted as an interpolated frame without any change. Alternatively, an average of the preceding and following frames is output.
However, when this interpolation process is applied to the smooth slow moving image interpolation playing, an image that is smoothly moving is displayed stopped around the scene change. For example, in 1/100× slow motion playing, 99 frames of interpolated images are generated between two frames of an original image. When the interpolated images are presented on a display device of 60 fps, the moving image stops for nearly two seconds and is unnaturally viewed.